The dimensions of modern wind turbine rotors (i.e. rotor diameters about 150 m and rotor weights about 50 tons) require the mounting of the wind turbine components in different steps. In particular, rotors are usually mounted after the mounting of the nacelle on the tower.
Some known rotor mounting methods use mobile cranes for lifting wind turbine rotors previously assembled on ground and mounting the whole assembly to the low speed shaft extending from the nacelle. These methods have become problematic because, on the one hand, the increasing size and weight of the wind turbine rotor, require expensive mobile cranes and, on the other hand, the surroundings of the wind turbine location sometimes limit or hinder the lifting of the complete rotor assembly from the ground because of its impracticability.
There are also known rotor mounting methods using mobile cranes for lifting the wind turbine rotor in several steps. For instance EP 1 507 975 discloses a method comprising a first step in which a sub-assembly of the hub with two blades is lifted and mounted and a second step in which the third blade is lifted and assembled to the hub.
There are also known rotor mounting methods using cranes installed on the wind turbine. EP 1 350 953 discloses a crane that uses one or two previously mounted sections of the tower as its support mast. Once said crane reaches an optimum height, carrying the corresponding component of the wind turbine, it tilts to set in place said component. WO 02/099278 discloses a lifting platform that moves along guide rails fixed to the wind turbine's tower.
There are also known rotor mounting methods for mounting the blades without using a crane. In the method disclosed in WO 2004/067954, it is used a cable—instead of a crane—fixed between a part of the hub and the ground and a blade can be mounted moving it upwards or dismounted moving it downwards along said cable. DE 20 2004 016460 discloses lifting means cooperating with a winch in ground which are mounted in the rotor hub in different positions for the lifting and mounting of each blade.
The costs of mobile and stationary cranes demand smaller and simpler crane systems for mounting wind turbine rotors.
The present invention is intended to satisfy this demand.